1. Field of the Invention
This invention pertains to the custom manufacture of dental and maxillo-facial prostheses utilizing a lost wax molding process and metal flasks for containing the materials during the process. The invention is a particularly useful improvement to the Hanau flask.
2. Description of the Related Art
Hanau flasks have been widely used in the manufacture of dental prostheses for about sixty years. The Hanau flask has a base, a body and a lid which fit together to define an easily removable container for dental prosthesis molding materials.
Patents relating to the molding of dental prostheses include the following:
______________________________________ U.S. Pat. No. Inventor Date ______________________________________ 2,378,633 House 1945 2,440,910 Opotow 1948 2,457,114 Amenta 1948 2,471,205 Fagan 1949 2,491,147 Zahn 1949 2,712,158 Villa 1955 3,635,630 Greene 1972. 3,663,141 Clenet et al 1972 4,119,292 Haker 1978. ______________________________________
House's patent describes a dental flask which includes U-shaped fillers 12 and 16 to facilitate removal of the dentures from the investment, and to adapt the flask to the making of various sizes of lower dentures. Opotow's flask has a C-shaped intermediate section with an open side, which is closed by a flange which extends down from the cover section. This design is to facilitate banking, and would not allow for increased height.
Amenta's patent describes the use of methyl methacrylate for making dental prostheses. A two-part flask is shown.
The Fagan patent describes a four-part dental flask that can only be used with all four parts. Fagan's lid also has a depending rear wall extending down from the lid, and an upwardly extending rear wall integral with the base. There are two intermediate body sections which complete the flask. Fagan's design is not intended to add height to his flask.
Zahn relates to the method of setting synthetic resin teeth in the denture base. Zahn's flask includes a base, a two-part body, a lid and spacer blocks. The bottom spacer block is integral with the base. Villa's two-part body is described having a continuous taper (Col 2, lines 69-72, Col 3, lines 1-3). A flask expander was not contemplated by Villa because it would distort the taper between Villa's two-part body section and create a ridge in the mold.
Greene's patent is directed to plastic inserts which fit within the flask members and which facilitate rapid curing of the plastic denture in a microwave oven. The outer flask comprises three parts: a lower flask member 20; an upper flask member 22; and a top flask member 34. The plastic inserts 52 and 54 are the actual mold container, and they do not include an expander.
Clenet et al describe a method for molding prostheses articles in which the two mold halves are stationary and firmly engaged. The flask member 10 is open on top and at one end and does not provide an enclosure for the mold. The size of the flask cavity is adjustable by means of a threaded rod 50. The rod 50 has a plastic clamping member 52 which engages the back of the model 40. This flask is entirely different from the Hanau type flask. Haker describes a mould which has removable retaining elements connected to it for holding the working model in the mould. Haker has no description of a flask.
Henry La Fuente et al describe a Hanau flask in which the body member has been cut into two sections to decrease the incidence of stone fracture which sometimes occurs using a 3-piece mold. See: La Fuente, et al, Modified denture flask for three-piece ear molds Jnl Prosthetic Dentistry 41:453 Apr. 1979.
None of the above references disclose a dental flask expander which may be placed on top of the base of the flask under the flask body when the mold is too high for the flask body. Use of the flask expander avoids a tedious extra step of grinding down the bottom of the mold to make it fit in the standard flask.